A device for detecting a line of sight or a point of gaze of a test subject in a non-contact manner has been considered important in the field of human interaction. If the high-precision line of sight detection technology is put to practical use, such device can be applied to various applications such as monitoring a driver, studying the level of interest in a certain product, and inputting data to a personal computer of a severely disabled person.
According to the line of sight detection methods disclosed in Patent Literature 1 and 2, a test subject is caused to gaze at a camera located in a known position and one point on a display screen located in a known position, and a function for calculating a line of sight direction of the test subject from the distance between the center of a pupil and a corneal reflection point is corrected, to detect the line of sight direction using the corrected function. These line of sight detection methods are capable of precisely detecting a line of sight, even when the test subject moves his/her head. The gaze detection method disclosed in Patent Literature 3 is a method for simultaneously detecting lines of sight of both eyes by using two cameras. According to this method as well, the test subject is required to look at the cameras in order to calibrate the results of detecting the lines of sight.
The reason that the test subject is required to look at the cameras in order to execute correction upon line of sight calculation is because a corneal reflection image of a light source is actually shifted from the center of each pupil although the corneal reflection image is ideally located in the center of each pupil due to the symmetry with respect to the optical axis of each eyeball. For this reason, when using the function to calculate the line of sight direction of the test subject from the distance |r|, the gain value included in the function cannot be accurately obtained unless so-called origin correction is executed. Each of the conventional technologies mentioned above, therefore, corrects the function by causing the test subject to gaze at a specified point including the position of the camera.